Mounting for piezo electric elements



Sept. 27, 1949.

v. E. BOTTOM 2,482,828

MOUNTING FOR PIEZOELEGIRIC ELEMENTS Filed April 5, 1945 FIG. 1.

INVENTOR. ViRG lL E. BOTTOM ATTORNEY Patented Sept. 27, 1949 UNITED STATES PATENT OFFICE I Virgil E. Bottom, Leonardo, N. J assignor to the United States of America as represented. by the Secretary of War Application April 3, 1945; SerialN0. 586,424.

5 Claims. (Cl. 1711'327.)

(Granted under the act ofi'March 3; 1883; asamended April30', 1928; 3'70 0. G. 757) 1 The invention described herein may be'manufactured and used by or for the Government for governmental purposes, without thepayment to me of any royalty thereon.

This invention. relates to piezo electric elements used in communication circuits forstabi-lizing the frequencies of master oscillators and filter cir cults; more'particularly, the invention relates to the mountings for such elements;

Crystal plates in the lower frequency range of crystal-controlled oscillators, such as from one to three mc., have been made -in'the past with an area of one squareinch ormore. This large size of the crystal plates has been necessary because of the method for mounting a crystal plate used heretofore,- which involved clamping it between two electrodes and holding it by its corners. Such a method of mounting a plate acted asan effective mechanical damping mechanism upon the crystal plate, and the only known method of obtaining the necessary amplitude of vibration with thecrystal plate mounted in this 'manner; and theconcomitant intensity of the electrical signal for controlling the oscillator, has been by increasing the'size of the plate until the desired activity was obtained insp-ite or the damping effect exerted by the mounting. Thus, for any given activity, the dimensions of a crystal could not be reduced beyond a certain minimum, this minimum being one square inch for one to three mo. crystal plates, as mentioned before.

The invention discloses a novel method of mounting a crystal plate uncla-mped, which 'elimie nates the damping effect exerted upon the plates by the known mountings. The unclamped mounting of the plate is accomplished by placing it-between two electrodes whichiare held in fixed relationship with. respect'to each other. and the plate by meansof three insulating. spacers. The advantages of suchmounting are two-fold; first, itispossible to obtainactivities with blanks. having an area of 6.3 square inch as great as those normally obtained with blanks having an area of one square inch mounted in the conventional pressure-mounted manner, thusresulting: in large conservation of quartz (66.7%), and, second, the 0.3 square inch blanks may be mounted in standard holders of much smaller size, thus satisfying stringent size requirements imposed upon numerous communication and remote control equipments. More specifically, the invention obtains the unclamped mode of mounting the plate by resorting to a three-point suspension for the electrodes of the piezo-electric plate which produces a crystal holder with greater mechanical and electrical stabilities' than the-stabilities obtainable with the known holders.

It is, therefore; an-object orthi-sinvention-to provide a novel, unclamped mounting for piezoelectric crystal plates in which the electrodesof the plate utilize a three-point suspensionm The novel features which are believed-tote characteristic of the invention are setforth the appended claims. Theinventionitself; how'- ever,-both-as to its organization-and method ot construction-,-together with further objects and advantages thereof, may best beunderstoodby reference to the'furt'herdescription in connec tio'n-with the accompanying drawing, in which:

Figure 1 is-anenlargedexploded-perspective view of a crystal holder and crystal .n'rountln g, and

Figure -2 isan enlarged, Vertical cross-sectional view of the holder-illustrated in- Fig. l,;with the elements in assembled relationship and the crosssection taken along line 2-2 shownin Fig.1. 7

Referring to the drawing, the crystal unitincludes a box it) made of any suitable, moistur resisting plastic, with-pins l2 and it solidly em bedded i-n-thelowerwa'll of the box. The pinslaresoldered to connectors l6} and i 8 which make 1305i: tive 'eleotr-ical contacts with the outersurfa'ces of electrode plates 29 and 22 as shown, more clearly in Fig. 2. Connector It is bent out in: Fig. 1', in order to-illustrate the inner shape of box It. The connectors it, N; are madeof verythin; easily flexible, rust proof alloy, and connector [6- is bent out, as shown in Fig. 1, for assembling the unit. Thepositiveel'ectrical contacts between theconnectors" l6, l8 and-theelectrodes 20 51122- are accomplished-by inserting a helical spring. 24 betwena'cover 26 andan insulating spacer 2%, the latter resting againstconnector it, .as shown in Fig. 2. Electrodes 2t and 22 are each provided with threeextensions: 3t, digital 1d 33', 34,35 which fit into -threerecesses in box lil; The elec* trodes are held in spaced relationship with respect to each other by means ofspacers 36, 31 and: 38 made of any'insulatin'g material having proper mechanical and electricalcharacteristics. Excel lent results: are obtainable with ceramic or glass; which have high leakage resistance, low cold flow, low dielectric loss, low temperature coefficients of expansion, and high coeflicient of hardness. A piezo-electric crystal plate 40 is mounted between the electrodes 20 and 22, as shown in Fig. 2. The horizontal dimensions of the elements, as they are illustrated in Fig. 2, have been exaggerated for illustrating the relative positions of the elements, and especially the fact that the thickness of the electrode spacers 36, 31 and 38 is greater than the thickness of the crystal plate 40, so that plate 40 is free to vibrate between the electrodes without being subjected to pressure by the electrodes, the plate being supported in its vertical position by the lower wall of box :9. The spacers 36, 3? and 38 must be thicker than the thickness of the crystal plate 40 by any amount up to one-hall the wave-length in air of the sound wave, generated by the vibrating crystal. The practical lower limit is set by the degree of flatness of the crystal plate, the spacers, and the electrodes, and any dust particles which may be between them The advantages of the disclosed type of mounting reside in the mechanical and electrical stabilities of the three-point suspension, small dielectric losses, and the ability to use smaller crystal plates in smaller holders without any loss in the available activities.

While the invention has been described with a reference to a particular embodiment of a crystal holder and mounting, it will be understood that various modifications of the apparatus shown may be made within the scope of the following claims.

What I claim is:

1. A piezo-electric unit including a piezoelectric plate, an electrode plate mounted on each side of said element, each of said electrode plates having three extensions protruding beyond the side area of said piezo-electric plate, the extensions of one electrode being in substantial register with the corresponding extensions of the other electrode plate, and a dielectric spacer inserted between each corresponding pair of said extensions, the thickness of said spacers being greater than the thickness of said piezo-electric plate, whereby said electrode plates form a free mounting for said piezo-electric plate, and said spacers form a three-point suspension for said electrode plates.

2. A mounting for a piezo-electric unit including a piezo-electric element, an electrode plate mounted on each side of said element, each of said electrode plates having three extensions protruding beyond the side area of said element, the extensions of one electrode plate being in substantial register with the corresponding extensions of the other electrode plate, a dielectric spacer inserted between each corresponding pair i of said extensions, the thickness of said spacers being greater than the thickness of said element, whereby said electrode plates form a free mounting for said element, and said spacers form a three-point suspension for said electrode plates, and mechanical instrumentalities for holding said electrode plates against said spacers and in fixed, spaced relationship with respect to each other.

3. A piezo-electric unit including a housing, an inner chamber, two spaced connectors mounted within said chamber, electrode plates held in a substantially fixed relationship with respect to said connectors by the inner walls of said chamber, said electrode plates being mounted between said connectors, a piezo-electric element between said plates, each of said plates having three extensions protruding beyond the side area of said piezo-electric element, the extensions of one plate being substantially in register with the corresponding extensions of the other plate, a dielectric spacer inserted between each corresponding pair of said extensions, the thickness of said spacers being greater than the thickness of said element, whereby said electrode plates form a free mounting for said element, and said spacers form a three-point suspension for said electrode plates, a cover for said chamber, and a spring mounted between said cover and one of said connectors for establishing pressure contacts between said electrode plates and said spacers, and pressure contacts between each connector and the corresponding electrode plate.

4. A piezo-electric unit as defined in claim 3 which further includes an insulating spacer mounted between said spring and the adjacent connector for insulating said spring and said cover from said adjacent connector.

5. A piezo-electric unit comprising a piezoelectric plate, two electrode plates on opposite sides respectively of said piezo-electric plate, each of said electrode plates including a body and three extensions, said body being of substantially the same shape and area as said piezoelectric plate and substantially in register therewith and said extensions being positioned about said body, the said extensions of the two electrode plates being substantially in register with each other, three dielectric spacers positioned between the corresponding pairs of extensions, the thickness of the spacers being greater than the thickness of the piezo-electric plate, a housing provided with a compartment having a central chamber and three recesses, said central chamber being of substantially the same shape as and slightly larger than the said piezo-electric plate and the three recesses being positioned about said central chamber, each of said recesses accommodating a pair of said extensions and one of said spacers, and means to hold the electrode plates and the spacers in intimate contact, the piezo-electric plate being restricted to a limited amount of lateral movement by the shape and size of the central chamber.

VIRGIL E. BOTTOM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,027,526 Franklin Jan. 14, 1936 2,038,804 Roosestein Apr. 28, 1936 2,123,236 'Fair July 12, 1938 2,329,321 Bach Sept. 14, 1943 2,394,999 Keller Feb. 19, 1946 FOREIGN PATENTS Number Country Date 499,225 Great Britain Jan. 20, 1939 

